Interposer assemblies electrically connect between densely spaced contact pads on adjacent parallel circuit members. Interposer assemblies are used wherever dense connections are required. The assemblies are particularly well suited for use in portable electronic devices such as cell phones, digital assistants, notebook computers and the like. The assemblies enable a reduction in the size and weight of the electronic devices.
The pads on the circuit members are arranged in identical patterns. Commonly, the circuit members are a circuit board and a ceramic plate carrying integrated circuits. The interposer assembly includes an insulating plate and a plurality of through-contacts carried in the plate and arranged in the same pattern as the pads on the circuit members. The contacts project above the top and bottom sides of the plate. The interposer assembly is sandwiched between the two members which are held together with the contacts forming electric connections between aligned pairs of pads.
Interposer assemblies form electrical connections between contact pads arranged in a very close proximity to each other. The pads may be arranged on a one millimeter center-to-center grid. Each assembly may have as many as 961 contacts. Four assemblies are conventionally mounted on a single frame with a total of 3,844 contacts in the frame.
In addition to requiring contacts which can be spaced very close to each other, the contacts must make reliable electrical connections with the pads during the lifetime of the electronic device. The circuit members may move towards and away from each other due to changes in operating temperature, handling of the device, or the like. The contacts must make reliable electrical connection with the pads despite the relative movement of the circuit members. Failure of a single contact to make a reliable connection may render the entire electronic device useless.
The individual electrical contact in the assembly acts as a spring that extends or compresses in response to the circuit members moving away or towards one another. The contact is compressed and deforms elastically when sandwiched between the contact pads. The contact must be able to extend outwardly when the circuit members move apart and compress when the circuit members move back together.
Interposer assemblies must occupy a minimum width between the circuit members. This requires that the individual electrical contacts in the assembly have a limited height. Yet the contacts must possess the required resiliency for maintaining reliable electrical contact with the pads throughout repeated cycles of extension and compression.
Further, the contacts must be compressed with a low mechanical closure force when the interposer assembly is sandwiched between the circuit members. Low closure force is required in order to prevent undue stress on the contact or a ceramic circuit member. A high closure force could distort or possibly break the contact or the ceramic member. Permanent distortion or deformation of the contact member may reduce or destroy the resiliency of the contact. The contact cannot lose resiliency to the extent that the contact is unable to maintain reliable electrical connections between the pads.
Conventional interposer assemblies use contacts which occupy a relatively large amount of space in the supporting plate making it difficult to meet closely spaced grid requirements. These assemblies are relatively expensive to manufacture and assemble.
Applicants' U.S. patent application Ser. No. 09/455,989, assigned to the assignee of the present invention, discloses an interposer assembly including metal through contacts loosely confined in closely spaced passages extending through an insulating plate. On rare occasions, contacts inserted into the passages in the above interposer assembly do not work properly.